In recent years, a fuel cell system which supplies power to a load, such as a mobile body, is reaching the phase of practical use. A fuel cell is adapted to take out an electromotive force by an electrochemical reaction between a fuel gas, such as hydrogen, and an oxidizing gas which contains oxygen. There is a predetermined relationship between an output current and an output voltage (an output current/output voltage characteristic). Such an output current/output voltage characteristic changes according to, for example, the gas amount of a fuel gas or an oxidizing gas supplied to the fuel cell. Further, on any output current/output voltage characteristic, an output current value which provides a maximum output power (net output) has been set. Here, the output power (allowed FC power) is a physical amount calculated by multiplying an output current by an output voltage, and has a characteristic based on a relationship with the amount of a gas supplied.
As a conventional related technique, there has been proposed a power source system equipped with means which stores an output power of a fuel cell (an allowed FC power) as an output characteristic indicating the relationship with a supplied gas amount, means which newly acquires the output characteristic and adds the acquired output characteristic to a memory, and means which determines an output power (allowed FC power) on the basis of the output characteristic stored in correspondence with the same gas amount (e.g., the publication of Japanese Patent Application Laid-Open No. 2003-272679 (paragraphs 0034, 0035, etc.).